The overall objectives of this project are to examine the effects of 2 weeks of bed rest on the sympathetic nerve responses to rhythmic and static forearm exercise. We postulate that sympathetic nerve responses will be increased because lactic acid production and forearm interstitial volume will be increased. We further postulate that forearm handgrip exercise and/or intermittant forearm compression will act as countermeasures to obviate the effects of bedrest. In the first year of the project, we will examine the effects of bedrest on the sympathetic nerve responses to: static exercises, rythmic forearm exercise and involuntary biceps contraction. Since increases in sympathetic discharge during static exercise are predominantly due to excitation of metaboreceptors, the experiments in static exercise will help determine if metaboreceptor activity is enhanced by bedrest. Experiments in rhythmic forearm exercise will be performed to examine whether mechanorecptor activity and/or central command activity is augmented by bedrest. The experiments in involuntary bicep contraction will be performed to determine whether mechanically-sensitive afferents in the human forearm are sensitized by the 2 week period of bedrest. State of the art human physiology techniques including microneurography and NMR will be used.